In late June 2008, just weeks before the opening of the Beijing Olympics, a massive green-tide occurred covering about 600km(2) along the coast of Qingdao, host city for Olympic sailing regatta. Coastal eutrophication was quickly attributed with the blame by the international media and some scientists. However, we explored an alternative hypothesis that the cause of the green-tide was due to the rapid expansion of Porphyra yezoensis aquaculture along the coastline over 180km away from Qingdao, and oceanographic conditions which favoured rapid growth of the bloom and contributed to transport of the bloom north into the Yellow Sea and then onshore northwest to Qingdao. At its peak offshore, the bloom covered 1200km(2) and affected 40,000km(2). This is the largest green-tide ever reported, the most extensive translocation of a green-tide and the first case of expansive seaweed aquaculture leading to a green-tide. Given similar oceanographic conditions to those that occurred in 2008, these green-tides may re-occur unless mitigation measures such as those proposed here are taken.